Injection molding cylindrical manifold insert and method

ABSTRACT

Injection molding apparatus and method wherein a number of cylindrical inserts or plugs each having a curved melt duct therethrough are accurately aligned and securely mounted in spaced cylindrical openings through a melt distribution manifold. An alignment and retaining pin made of a very strong material extends from a bore in the manifold into a bore in the insert. The manifold is heated and the inserts and pins are cooled prior to insertion into place to provide very tight fits when they are at the same temperature which very accurately aligns the melt ducts through the inserts. The combination of the inserts fitting tightly in the openings and the strength of the pins is sufficient to withstand the rearward forces from the pressurized melt being injected through the curved melt ducts to retain the inserts in place.

BACKGROUND OF THE INVENTION

This invention relates generally to injection molding apparatus and amethod of making it and more particularly to such apparatus and methodwherein a number of cylindrical inserts each having a curved melt ductextending therethrough are each securely seated in a predeterminedposition in one of a plurality of spaced transverse openings extendingthrough a melt distribution manifold.

Injection molding apparatus having a heated melt distribution manifoldand a plurality of spaced heated nozzles each conveying melt to adifferent gate are well known. The melt distribution manifold has a meltpassage with a number of branches extending outwardly from a commoninlet portion to convey the melt to the spaced heated nozzles. Eachnozzle has a central melt bore extending at 90° to the branches of themelt passage in the melt distribution manifold. It is also known to seatinserts or plugs in transverse openings extending through the meltdistribution manifold in alignment with the nozzles. Each insert has amelt duct with a smoothly curved bend extending through 90° from aninlet in alignment with a respective branch of the melt passage in themelt distribution manifold to an outlet in alignment with the melt borethrough an aligned nozzle.

In order to avoid color change problems and stress in the melt it iscritical that the melt duct through each insert be very accuratelyaligned with the respective branch of the melt passage and the centralmelt bore through the respective nozzle. It is also important that theinsert be secured in place to withstand rearward forces from thepressurized melt flowing through the bend in the melt duct. Mold-MastersLimited, Canadian Patent Application Serial Number 2,047,461 laid openJan. 20, 1993 entitled "Injection Molding Manifold with RemovableInserts" shows inserts which are aligned by alignment pins and aretapered to withstand the force of the melt flowing through the curvedmelt ducts. U.S. Pat. No. 5,366,369 to Gellert which issued Nov. 22,1994 shows inserts having outer flange portions to securely retain themin place against these same forces. However, these previous inserts havethe disadvantages that they are relatively costly to make and slightmisalignment remains a problem, particularly when molding some modernmaterials which are very shear sensitive.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to at leastpartially overcome the disadvantages of the prior art by providinginjection molding apparatus which is easier to make and an improvedmethod of accurately mounting the inserts and securely retaining them inplace.

To this end, in one of its aspects, the invention provides an injectionmolding apparatus having a heated melt distribution manifold and aplurality of spaced heated nozzles seated in a mold. Each of the heatednozzles have a melt bore extending therethrough to convey melt to a gateleading to a cavity. The melt distribution manifold has a melt passageand a plurality of spaced transverse openings extending therethroughwith each transverse opening aligned with one of the nozzles. The meltpassage has a plurality of branches extending outwardly from a commoninlet portion towards each of the nozzles. A plurality of inserts orplugs each have a rear face, a front face, an outer surface, and a meltduct extending therethrough. Each insert is received in one of thetransverse openings in the melt distribution manifold with its faceabutting against the rear end of a respective nozzle. The melt duct hasa smoothly curved bend extending through substantially 90° from an inleton the outer surface in matching alignment with one of the branches ofthe melt passage in the melt distribution manifold to an outlet on thefront face in matching alignment with the melt bore through therespective nozzle. Each transverse opening in the melt distributionmanifold is cylindrical. The outer surface of each insert is cylindricaland fits tightly in said one of the transverse openings in the meltdistribution manifold. Each insert has an alignment and retaining pin orplug fitting tightly in a retaining pin bore in the melt distributionmanifold and an aligned alignment and retaining pin bore in the insert.

In another of its aspects, the invention further provides a method ofmaking injection molding apparatus having a melt distribution manifoldwith a plurality of spaced transverse openings therethrough and a meltpassage having a plurality of branches extending outwardly from a commoninlet portion to the plurality of spaced transverse openings. A numberof inserts each have an outer surface and a melt duct with a smoothlycurved bend extending therethrough from an inlet on the outer surface.Each insert is seated in one of the transverse openings in the meltdistribution manifold with the inlet to the melt duct in alignment withone of the branches of the melt passage in the melt distributionmanifold. The melt distribution manifold is made with the transverseopenings and the melt passage, and the inserts are made with the meltducts. Each insert is inserted into one of the transverse openings withthe inlet to the melt duct in each insert in alignment with one of thebranches of the melt passage in the melt distribution manifold. Thespaced transverse openings through the melt distribution manifold aremade cylindrical. The inserts with their outer surfaces cylindrical tofit tightly in the transverse openings through the melt distributionmanifold when the inserts and the melt distribution manifold are at thesame temperature. An alignment and retaining pin bore is machinedextending through the melt distribution manifold to each transverseopening. A matching alignment and retaining pin bore is machined in eachinsert extending radially inward from the outer surface of the insertopposite from and in alignment with the inlet to the melt duct.Alignment and retaining pins are made to fit tightly in the alignmentand retaining pin bores in the melt distribution manifold and eachinsert when the inserts and the melt distribution manifold are at thesame temperature. The melt distribution manifold is heated to apredetermined temperature. The inserts and alignment and retaining pinsare cooled to a predetermined temperature. Each cooled insert is theninserted into one of the transverse openings in the heated meltdistribution manifold with the alignment and retaining pin bore in thecooled insert aligned with the alignment and retaining pin bore in theheated melt distribution manifold. One of the cooled alignment andretaining pins is then inserted to extend through the alignment andretaining pin bore in the heated melt distribution manifold into thealigned alignment and retaining pin bore in each cooled insert. Thus,when the inserts and the melt distribution manifold are at the sametemperature, the tight fits of the inserts in the transverse openingsand the alignment and retaining pins in the alignment and retainingbores in the inserts and the melt distribution manifold both accuratelyalign and securely retain the inserts in place.

Further objects and advantages of the invention will appear from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a portion of an injection molding systemshowing a melt distribution manifold with two inserts according to oneembodiment of the invention,

FIG. 2 is an isometric view of the insert seen on the right in FIG. 1,

FIG. 3 is an isometric view of the insert seen on the left in FIG. 1,and

FIGS. 4-6 are sectional views showing different steps in a method ofmounting the inserts in a melt distribution manifold according toanother embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made to FIG. 1 which shows a portion of an injectionmolding system or apparatus with a melt passage 10 having branches 12which extend outwardly in a steel melt distribution manifold 14 from acentral inlet portion 16 to a shorter nozzle 18 and a longer nozzle 20.The melt passage 10 extends through a central melt bore 22 in eachnozzle 18, 20 to gates 24 leading to a cavity 26. While only a singlecavity 26 is shown, in other embodiments each gate 24 can lead to aseparate cavity. While the melt distribution manifold 14 and only thetwo steel nozzles 18, 20 are shown mounted in a mold 28 for ease ofillustration, an injection molding system will normally have many morenozzles 18, 20 with melt passage branches 12 extending to them.Similarly, while the mold 28 can have a greater number of platesdepending upon the application, in this case, only a nozzle retainerplate 30 and a back plate 32 secured together by bolts 34, as well as acavity retainer plate 36 are shown for ease of illustration.

The melt distribution manifold 14 has a central inlet portion 38surrounded by a locating ring 40 and is heated by an integral electricalheating element 42. The melt distribution manifold 14 is mounted betweenthe nozzle retainer plate 30 and the back plate 32 by a central manifoldlocator 44 and a number of pressure discs 46 which provide an insulativeair space 48 between the heated manifold 14 and the surrounding mold 28,which is cooled by pumping a cooling fluid such as water through coolingconduits 50. The melt distribution manifold 14 is accurately aligned inplace by a locating pin 52 extending outwardly into a cam 54 seated inthe nozzle retainer plate 30.

Each of the heated nozzles 18, 20 has an integral electrical heatingelement 56 extending around the central melt bore 22. In thisembodiment, each of the heated nozzles 18, 20 also has a gate insert 58mounted at its front end 60 with the gate 24 extending therethrough tothe cavity 26. The shorter heated nozzle 18 also has a flange portion 62which fits in a circular seat 64 in the nozzle retainer plate 30. Thislocates the short heated nozzle 18 with an insulative air space 66extending between it and the surrounding cooled mold 28. As describedbelow, the longer heated nozzle 20 is also mounted with an insulativeair space 68 extending between it and the surrounding cooled mold 28.

Also referring to FIGS. 2 and 3, the melt distribution manifold 14 has anumber of spaced cylindrical transverse openings 70, 72 extendingtherethrough with steel inserts or plugs 74, 76 received in them inalignment with the heated nozzles 18, 20. Each of the inserts 74, 76 hasa rear face 78, a front face 80 and a cylindrical outer surface 82 whichfits tightly in one of the cylindrical transverse openings 70, 72. Eachof the inserts 74, 76 also has a melt duct 84 with a smoothly curvedbend which extends through substantially 90° from an inlet 86 on thecylindrical outer surface 82. The melt duct 84 forms part of the meltpassage 10 to convey melt from a respective branch 12 of the meltpassage 10 to the melt bore 22 through the respective aligned nozzle 18,20. In the embodiment shown, the insert 74 in the transverse opening 70on the right in FIG. 1 with its front face 80 abutting against the rearend 88 of the shorter nozzle 18 is shorter than the insert 76 in thetransverse opening 72 on the left. This difference in lengths of theinserts 74, 76 allows nozzles 18, 20 of standard lengths to be used toaccommodate different distances between the melt distribution manifold14 and the various gates 24. As can be seen, in this embodiment, thelonger insert 76 has a threaded opening 90 extending from its front face80 into which a threaded rear portion 92 of the longer nozzle 20 isscrewed. This ensures the melt bore 22 in the longer nozzle 20 isaligned with the curved melt duct 84 through the insert 76 and, togetherwith the gate insert 58 at its front end 60, locates the longer nozzle20 with the insulative air space 68 extending around it.

Each of the inserts 74, 76 has an alignment and retaining pin or plug 94which fits tightly in an alignment and retaining pin bore 96 in the meltdistribution manifold 14 and an alignment and retaining pin bore 98extending radially inward from the cylindrical outer surface 82 of eachof the inserts 74, 76. In this embodiment, each alignment and retainingpin bore 96 in the melt distribution manifold 14 is a continuation ofone of the branches 12 of the melt passage 10. The alignment andretaining pin bore 98 in each of the inserts 74, 76 is opposite from andin alignment with the inlet 86 to its melt duct 84. The alignment andretaining pins 94 are made of a very strong material such as hardenedtool steel. Thus, the combination of the inserts 74, 76 fitting tightlyin the transverse openings 70, 72 and the strength of the alignment andretaining pins 94 is sufficient to withstand the rearward forcesgenerated from the pressurized melt being injected through the curvedmelt ducts 84 and retain the inserts 74, 76 in place.

In this embodiment, each of the inserts 74, 76 also has a prealignmentpin 100 which extends from an opening 102 in the melt distributionmanifold 14 into a prealignment pin bore 104 in each of the inserts 74,76. The prealignment pins 100 do not fit tightly, and the purpose ofthem is to approximately prealign the alignment and retaining bore 98 ineach of the inserts 74, 76 with the alignment and retaining bore 96 inthe melt distribution manifold 14 to facilitate insertion of the coldinserts 74, 76 and the alignment and retaining pins 94 in the hot meltdistribution manifold 14.

Reference is now also made to FIGS. 4-6 to describe the method of makingthe system of apparatus according to one embodiment of the invention.While only a portion of the melt distribution manifold 14 and the insert74 on the right in FIG. 1 are shown for ease of illustration, it will beunderstood that the method is the same for both inserts 74, 76. A steelmelt distribution manifold 14 is made having the integral electricalheating element 42 and a number of the spaced transverse cylindricalopenings 70, 72 extending therethrough. A corresponding number of steelinserts 74, 76 having cylindrical outer surfaces 82 and predeterminedlengths are made to fit tightly in the transverse openings 70, 72 in themelt distribution manifold 14 when the inserts 74, 76 and the meltdistribution manifold 14 are at the same temperature. The inserts 74, 76can be the same length or can have different lengths as shown in FIG. 1to allow for different distances between the melt distribution manifold14 and the different gates. The melt distribution manifold 14 ismachined to provide the alignment and retaining pin bore 96 extending toeach transverse opening 70, 72. As mentioned above, this bore 96 isusually a continuation of one of the branches 12 of the melt passage 10.Each of the inserts 74, 76 is machined to provide a matching alignmentand retaining pin bore 98 extending radially inward from its outersurface 82 opposite from and in alignment with the inlet 86 to the meltduct 84.

Alignment and retaining pins 94 are made of a suitable strong materialsuch as hardened tool steel to fit tightly in the alignment andretaining pin bores 96, 98 in the melt distribution manifold 14 and theinserts 74, 76 when the melt distribution manifold 14 and the inserts74, 76 are at the same temperature. The melt distribution manifold 14 isheated in an oven to a suitable temperature of approximately 230° C. Theinserts 74, 76 with the prealignment pins 100 inserted into theprealignment pin bores 104 and the alignment and retaining pins 94 areinserted into a bath 106 of a suitable material such as liquid nitrogento cool them to a temperature of approximately -100° C. The cooledinserts 74, 76 are quickly inserted into the transverse openings 70, 72in the heated melt distribution manifold 14 with the prealignment pins100 received in the prealignment pin openings 102 in the meltdistribution manifold 14. A cooled alignment and retaining pin 94 isalso quickly inserted through the alignment and retaining pin bore 96 inthe heated melt distribution manifold 14 into the alignment andretaining pin bore 98 in each of the cooled inserts 74, 76. When themelt distribution manifold 14 cools off and the inserts 74, 76 andalignment and retaining pins 94 warm up to the same temperature, thetransverse openings 70, 72 contract and the inserts 74, 76 and thealignment and retaining pins 94 expand. This results in the alignmentand retaining pins 94 fitting very tightly in the alignment andretaining pin bores 96 in the melt distribution manifold 14 and theinserts 74, 76 fitting very tightly in the transverse openings 70, 72 inthe melt distribution manifold 14. The very tight fit of the alignmentand retaining pins 94 in the alignment and retaining pin bores 96provides very accurate alignment of the melt ducts 84 in the inserts 74,76 with the branches 12 of the melt passage 10 and the melt bores 22through the nozzles 18, 20. As mentioned above, the combination of theinserts 74, 76 fitting tightly in the transverse openings 70, 72 and thestrength of the alignment and retaining pins 94 is sufficient towithstand the rearward forces from the pressurized melt being injectedthrough the curved melt ducts 84 to retain the inserts 74, 76 in place.

In use, the system is assembled as shown in FIG. 1 with the inserts 74,76 secured in the respective transverse openings 70, 72 in the meltdistribution manifold 14. After assembly, electrical power is applied tothe electrical heating elements 42, 56 in the melt distribution manifold14 and the nozzles 18, 20 to heat the melt distribution manifold 14 andthe nozzles 18, 20 to a predetermined operating temperature. Pressurizedmelt is then applied from a molding machine (not shown) to a centralinlet 108 of the melt passage 10 according to a predetermined cycle. Themelt flows through the inserts 74, 76, nozzles 18, 20 and gates 24 intothe cavity 26. After the cavity 26 is filled and a suitable packing andcooling period has expired, injection pressure is released. The mold 28is then opened to eject the molded product. After ejection, the mold 28is closed and the cycle is repeated continuously every 15 to 30 secondswith a frequency depending upon the wall thickness and the number andsize of the cavities 26 and the exact material being molded.

While the description of the hot runner injection molding apparatus andmethod with inserts 74, 76 accurately and securely mounted in spacedtransverse openings through the melt distribution manifold 14 has beengiven with respect to preferred embodiments, it will be evident thatvarious modifications are possible without departing from the scope ofthe invention as understood by those skilled in the art and as definedin the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed is defined as follows:
 1. In an injection moldingapparatus having a heated melt distribution manifold and a plurality ofspaced heated nozzles seated in a mold, each of the heated nozzleshaving a melt bore extending therethrough to convey melt to a gateleading to a cavity, the melt distribution manifold having a meltpassage and a plurality of spaced transverse openings extendingtherethrough, each transverse opening aligned with one of the nozzles,the melt passage having a plurality of branches extending outwardly froma common inlet portion towards each of the nozzles, and a plurality ofinserts each having a rear face, a front face, an outer surface, and amelt duct extending therethrough, each insert being received in one ofthe transverse openings in the melt distribution manifold with the frontface abutting against the rear end of a respective nozzle, the melt ducthaving a smoothly curved bend extending through substantially 90° froman inlet on the outer surface in matching alignment with one of thebranches of the melt passage in the melt distribution manifold to anoutlet on the front face in matching alignment with the melt borethrough the respective nozzle, having the improvement wherein;(a) eachtransverse opening in the melt distribution manifold is cylindrical andthe outer surface of each insert is cylindrical and fits tightly in saidone of the transverse openings in the melt distribution manifold, and(b) each insert has a prealignment pin and an alignment and retainingpin, the prealignment pin extending from an opening in the meltdistribution manifold into an aligned bore in the insert, and thealignment and retaining pin fitting tightly in a retaining pin bore inthe melt distribution manifold and an aligned alignment and retainingpin bore in the insert.
 2. Injection molding apparatus as claimed inclaim 1 wherein the alignment and retaining pin bore in each insertextends radially inward from the outer surface opposite from and inalignment with the inlet to the melt duct.
 3. Injection moldingapparatus as claimed in claim 2 wherein the alignment and retaining pinsare made of hardened tool steel.
 4. Injection molding apparatus asclaimed in claim 3 wherein at least two of the inserts have differentlengths.